A geomagnetic storm affects the dynamics and composition of the ionosphere and also offers an excellent opportunity to study the plasma dynamics. In the present study, we have used the VHF scintillations data recorded at low latitude Indian station Varanasi (Geomag. latitude $=$ 14$^{\circ}$55$'$N, long. $=$ 154$^{\circ}$E) which is radiated at 250 MHz from geostationary satellite UFO-02 during the period 2011–2012 to investigate the effects of geomagnetic storms on VHF scintillation.Various geomagnetic and solar indices such as Dst index, Kpindex, IMF Bz and solar wind velocity (Vx) are used to describe the geomagnetic field variation observed during geomagnetic storm periods. These indices are very helpful to find out the proper investigation and possible interrelation between geomagnetic storms and observed VHF scintillation. The pre-midnight scintillation is sometimes observed when the main phase of geomagnetic storm corresponds to the pre-midnight period. It is observed that for geomagnetic storms for which the recovery phase starts post-midnight, the probability ofoccurrence of irregularities is enhanced during this time and extends to early morning hours.

The occurrence of total 113 geomagnetic storms during declining phase of Solar Cycle 24 (2015–2017) subdivided as about 105 moderate storms (${\rm Dst} = −50$ nT to $−$100 nT), 6 intense storms (${\rm Dst} = −100$ nTto $−$200 nT) and 2 severe storms (Dst < $−$200 nT) has been diagnosed on the basis of 5 day active window through the CACTus (Computer aided CME tracking) software. A detailed study has been carried out for the 6intense and 2 severe storms. It is inferred that CMEs are the major source of geomagnetic storms to occur. Out of the 6 intense and 2 severe storms, only 1 has been observed with the origin of CIR. Thus, all analyzed intensegeomagnetic storms are due to coronal mass ejection at the Sun. Most of our results are in good accordance with other reported results.

Journal of Astrophysics and Astronomy

Journal of Astrophysics and Astronomy | News

Continuous Article Publication

Posted on January 27, 2016

Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.